Originally Posted By: adam2
I would advise against refilling gas cylinders that are intended to be disposable.

When a container is filled, it is most important that it is not completly full, in order to allow room for expansion.
If the container is overfilled, then even a modest increase in temperature may cause it to burst.

There is also the risk of filling a butane container with propane or with a butane/propane mix which has a higher pressure.

The risks may be somwhat reduced by
Only filling on a hot day, in order that subsequent temperature increases are unlikely.
Only partialy filling
Keeping re-filled containers outdoors
Not keeping them long term.

Refilling should be done, if at all, outdoors due to the risk of leakage.

The best advice though, IMO is dont.
Adam,

I wonder, did you read my blog post at all?

I specifically addressed overfilling. I specifically addressed the proper mix of gasses. I specifically addressed safe vapor pressure.

Originally Posted By: adam2
AFAIK in some states of the USA it is a federal offence to transport refilled disposable gas canisters.
If it varies state to state, then it is not a Federal offense. The US Department of Transportation (DOT) regulates interstate commerce. Transportation across state lines is within their jurisdiction, and my understanding is that DOT does prohibit such transport. I so state in my blog post.

HJ
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Adventures In Stoving